The present invention relates to a belt tensioner for an automotive engine and a method for mounting the same.
Timing belt tensioners, such as the tensioners described in U.S. Pat. No. 4,824,421, entitled: xe2x80x9cBelt Tensioner with Releasable Belt Damping Loadsxe2x80x9d, hereby incorporated by reference, are mounted directly onto the vehicle engine block. The standard procedure for installing such tensioners is to tighten the mounting bolt to finger tightness, train the belt around the tensioner, adjust the tensioner arm position relative to the nominal position so that the tensioner is in desired tensioning engagement with the belt, and then fully tighten the mounting bolt.
The current procedure for mounting timing belt tensioners is not always satisfactory for a number of reasons. First, tightening of the mounting bolt after adjusting the tensioner arm causes motion of the pivot shaft thereby reducing the accuracy of the adjusted position of the tensioner and thus the pre-load of the tensioner. Second, the mounting bolt is not fully tightened when the tensioner is initially moved into desired tensioning engagement with the belt, and therefore the bolt will tilt under the force of the belt. When the mounting bolt is tightened, it will move to be fully perpendicular to the engine mounting surface, altering the desired static tension that the tensioner applies to the belt. Third, in removing the tensioner for repair or replacement, the belt load will act on the tensioner as the mounting bolt is being removed, resulting in damage to the screw threads of the mounting bore on the tensioner mount.
The disadvantages of the prior art may be overcome by providing a belt tensioner for an automotive engine, wherein the tensioner pivot shaft is mounted in such a manner that it is firmly mounted on the engine without tilting, before and during installation adjustment, and during normal engine operation. In addition, the tensioner pivot shaft can be manually adjusted during installation to permit proper tensioning of the belt.
The present invention also provides a method for mounting a tensioner whereby the tensioner is firmly mounted to the engine prior to adjustment for pre-loading the tensioner into tensioning engagement with the belt.
According to one aspect of the invention, there is provided a tensioner, a stepped mounting bolt and a spring washer. The mounting bolt is inserted through the spring washer and then inserted through the tensioner and firmly tightened a predetermined amount to clamp the tensioner to a tensioner mounting surface. The bias of the spring washer produces a predetermined frictional torque resistant force which secures the tensioner in place before adjustment and during normal engine operation while allowing a limited amount of angular rotation of the pivot shaft to nominally bias the tensioner against the timing belt.
In accordance with another aspect of the invention, there is provided a belt tensioner for tensioning a belt for a motor vehicle, comprising a pivot shaft, a pivoting structure mounted for pivotal movement on the pivot shaft, and a pulley mounted for rotation on the pivoting structure. A spring biases the pivoting structure in a direction that moves the pulley mounted on the pivoting structure into tensioning engagement with the belt. A bolt is constructed and arranged to mount the belt tensioner on the motor vehicle engine mount. The bolt is constructed and arranged to be tightened to a predetermined extent for installing the tensioner of the motor vehicle. The predetermined extent is the same extent to which the bolt is tightened during normal operation of the tensioner. A clamping structure applies a predetermined clamping force on the pivot shaft after the bolt is tightened to the predetermined extent. The predetermined clamping force is sufficiently large to maintain the pivot shaft in perpendicular relation to the engine mount and prevent tilting of the pivot shaft when the tensioner is moved into installed tensioning engagement with the belt, yet sufficiently small to permit manual movement of the pivot shaft relative to the mounting bolt for adjusting the amount of tension applied by the tensioner to the belt.
A further aspect of the invention relates to a belt tensioner wherein the bolt comprises a shoulder that limits tightening of the bolt to a predetermined extent.
A further aspect of the invention relates to a method for installing a belt tensioner for tensioning a belt for a motor vehicle. The method comprises a pivot shaft and a pivoting structure mounted for pivotal movement on the pivot shaft. A pulley is mounted for rotation on the pivoting structure with a spring biasing the pivoting structure in a direction that moves the pulley mounted on the pivoting structure into tensioning engagement with the belt. A bolt is constructed and arranged to mount the belt tensioner on the motor vehicle engine mount; and a clamping structure. The method further comprises mounting the tensioner on the motor vehicle engine with the bolt; tightening the bolt so that the clamping structure applies a predetermined clamping force on the pivot shaft, which predetermined clamping force is sufficiently large to maintain the pivot shaft in perpendicular relation to the engine mount and prevent tilting of the pivot shaft when the tensioner is moved into installed tensioning engagement with the belt, yet sufficiently small to permit manual movement of the pivot shaft relative to the mounting bolt for adjusting the amount of tension applied by the tensioner to the belt.
Other objects and advantages of the present invention will become apparent from the following detailed description and appended drawings illustrating the preferred embodiments.